In the concrete industry, “screeding-boards” are common tools used to level concrete that has been freshly poured. For the purposes of this specification and the claims contained herein, the term “plastic concrete” shall refer to freshly-poured concrete that has not yet set up and hardened.
The types of screeds used in leveling plastic concrete vary from a 2×4 plank of wood, which is manually pushed or pulled through the concrete to a mechanical screed, which is gas and occasionally electrically powered. Often, the type of screed used depends upon the size and complexity of the surface area to be leveled. Conventional manual and power screeds have their distinct problems.
Power screeds are commonly used only for larger spaces and lack the versatility required to screed concrete in smaller spaces, such as doorframes, concrete pedestals, or floors with pipes and/or trenches. Mechanical screeds are often too expensive and bulky for the average individual to use (such as in a home-renovation project).
Manual screeds continue to be used in the majority of concrete projects. Manual screeds are necessarily used for small surface areas, slopes and around difficult spaces such as drains and columns. However, manual screeds are labourious to use and difficult to maneuver through the concrete. Manual screeds are also problematic due to difficulties in consistently and accurately maintaining the screed level throughout the screeding process.
The conventional method of guiding manual screeds is relatively inaccurate. Manual screed operators usually use string lines and, in large commercial projects, perhaps a laser leveling system to create reference guides in the plastic concrete and then attempt to move the screed blade on the guides to produce a flat and level floor. The laser leveling system usually comprises a reference laser and a laser receiver mounted on a post. Once the receiver is leveled relative to the reference laser, the foot of the post is at the desired concrete height. The post is then used to establish guide pins in the plastic concrete indicating the desired concrete height. The concrete is screeded using these guides.
Various attempts have been made to increase the accuracy of portable screeds by attaching a component of the laser leveling system directly to the portable screed. These are discussed below.
U.S. Pat. No. 4,752,156 provides a portable screed comprising: a stationary laser projector, which is separate from the screed, and a laser receiver, which is adjustably mounted on to the screed itself. The receiver can be vertically adjusted to receive the signal at different heights. The screed also contains a sight-level included on the screed for leveling of the entire screed. However, this reference fails to teach the use of an inclinometer for screeding sloped surfaces at different angles because the laser transmitter is stationary.
U.S. Pat. No. 5,288,166 involves a laser-operated automatic grade control system, having a laser projector and a laser receiver, which automatically detects elevation relative to the laser and adjusts the height of the finishing tool via an adjustable hydraulic cylinder. However, the system taught by this reference is too large to be used on sloped surfaces.
U.S. Pat. No. 6,758,631 provides a portable screed guidance system. Mounted on the screed are inclination measuring device(s) and leveling device components(s) (e.g. laser sensor) for measuring height relative to a stationary reference laser signal positioned in the worksite. This device is not suitable for use in leveling plastic concrete in confined spaces.
U.S. Pat. No. 6,089,787 Allen et al. provides a mechanical vibrating portable screed having laser sensors positioned on the screed. The screed derives elevation information from a remote laser, in response to which the gradient may be adjusted automatically or by the screed operator. This screed is bulky and does not provide a means for screeding on slopes of varying degrees or in small areas.
Plastic concrete can be screeded through the use of concrete elevation pins placed throughout the surface where concrete is to be poured. Screeding off elevation pins can be problematic in that costly time can be lost in correctly placing and re-adjusting the pins. Moreover, conventional laser systems provide only horizontal measurements and are not useful where screeding sloped concrete surfaces is required.
There is a need for a concrete-leveling system that can be used in small spaces and that is easy to control and comfortable to maneuver. The use of traditional hand screeds, having no handles or handles of rectangular shape, results in hand and finger injury, in missed work due to injury and in poor workmanship due to fatigue from using the traditional screed board.
It is, therefore, desirable to have a concrete-leveling system that overcomes the shortcomings of the prior art and the problems discussed above.